1. Field of the Invention
The present invention relates to a wireless communication apparatus and a method using the same to transmit data, and more particularly to a wireless communication apparatus and a method thereof capable of selectively transmitting data of a certain packet type. The present application is based on Korean Patent Application No. 2001-78273, filed Dec. 11, 2001, which is incorporated herein by reference.
2. Description of the Related Art
Infrared data association (IrDA), wireless LAN (IEEE802.11), Bluetooth and shared wireless access protocol (SWAP) are well-known technologies of remote wireless data communication.
Among these, Bluetooth is a code name of wireless communication technology that covers various fields like electric communication, networking, computing, and consumer goods. In Bluetooth technology, a connection of multiple cables within short distances is substituted with one wireless connection. For example, the Bluetooth wireless technology applied in the mobile phone and laptop computer enables the use of the mobile phone and laptop in connection with each other without a cable. The Bluetooth system can include almost all digital devices, such as printers, personal digital assistants (PDA), desktop computers, faxes, keyboards and joysticks or the like.
Generally, Bluetooth covers a maximum of 10 m of transmittable distance at a maximum 1 Mbps of data transmission speed. The transmission speed of 1 Mbps is achieved easily and cheaply in the industrial scientific medical (ISM) frequency band of 2.4 GHz which is permitted to be used without any license. The distance of 10 m is enough to reach from the desktop computer in the office to the portable device. Bluetooth is made to operate efficiently in a radio frequency environment where there is a lot of noise. Thus, Bluetooth adopts a frequency hopping 1600 times per second, to enable stable data transmission even in the wireless frequency band where there is a lot of noise. The frequency hopping is one of the spread spectrum technologies like the direct sequence. However, the frequency hopping distinguishes from the direct sequence in that the carrier signal is transmitted, changing the frequencies many times in every second.
In addition to one-to-one communication, the Bluetooth system also supports one-to-multi communication. As shown in FIG. 1, in the Bluetooth system, several piconets can be constructed and connected with each other. Here, the respective piconets are distinguished from each other by a frequency hopping order. The piconet is formed with one master and more than one slave, and serves as a basic unit of the Bluetooth system. One piconet can include one master and a maximum of seven (7) slaves. Basically, the master and the slaves communicate bi-directionally using a time division duplex (TDD) based on a basic unit of one (1) hopping slot of 625 μs (625 μs= 1/1600 sec). The network connected with a plurality of piconets altogether is called a ‘scatternet’.
FIG. 2 is a view showing communication between the master and slaves based on the TDD. Referring to FIG. 2, one channel, which is allotted to a time slot, is 625 μs long. The number of time slots is determined according to the Bluetooth clock of the master of the piconet. Also, the master and the slaves can transmit a packet using the time slot. In other words, the master transmits the packet when the time slots are even-number, while the slaves transmit the packet when the time slots are odd-number. Further, the packet intended to be transmitted from the master or the slaves has to be within five (5) time slots. In a transmission of multiple slots, the hopping frequency of the time slot where the packet is initially transmitted, is continuously used for all the packets. Here, the ‘packet’ is the unit of data transmitted in the piconet channel.
Each packet consists of three segments, that is, access code, header and payload. The access code is used to detect the existence of a packet and to transmit the packet to a particular device. The header contains control information concerning the packet and link, such as the slave address intended by the packet. The payload contains message information when the message from the logical link controller and adaptation protocol (L2CAP) or from the link manager (LM) is an upper layer protocol message, and contains data when the message from the L2CAP or from the LM is the data stored in a stack.
The access code and the header have fixed size, usually 72 bits and 54 bits, respectively. The payload is comprised of 0 through 2745 bits. In order to ensure a time for the transmitting/receiving devices to tune the frequency of the channel, however, the size of the packet should be limited to 366 bits. Also, since the packet header needs to be included in the packet, the payload can use only 216 bits. When the forward error correction (FEC) is used for the error correction, due to error code, only 136 bits can be used as the available payload. Among the packet types that use only one slot in the asynchronous connectionless link (ACL), the packet type that does not use the FEC is called ‘DH1 (Data-High rate, 1 slot)’, while the packet type that uses the FEC is called ‘DM1 (Data-Medium rate, 1 slot)’. Since the DH packet does not use the FEC for an error correction, it has a higher transmission rate than the DM packet. Here, the ‘ACL connection’ refers to a link used by the Bluetooth system for a data transmission.
For a more efficient data transmission, Bluetooth defines the types of the packets according to the numbers of slots they use: the packet type that uses three (3) slots is DH3 packet type, and the packet that uses five (5) slots is DH5 packet type. The DH3 and DH5 packet types are more efficient since they transmit a lot more information for one slot than the DH1 packet type does. There are DM3 and DM5 corresponding to the DM1. The DM1 packet only transmits data information. As described above, there are six (6) types of packets for data transmission, and each packet type is distinguished from each other by the length and whether it corrects the error or not. The six packet types are shown in the Table 1 below:
TABLE 1TypeMaximum Payload (byte)FECMaximum Rates (Kbps)DM1170108.8DH127X172.8DM31210387.2DH3183X585.6DM52240477.8DH5339X723.2
According to the error rate of the channel, each of the six (6) packet types for data transmission shows different performance. In the case of no error occurrence, the DH5 packet type proves most efficient since the DH5 type can transmit the largest information in a unit slot. If there is increased bit error rate, the error rate of the DH5 packet type increases more rapidly than the error rates of other packet types of smaller sizes. In other words, the packet of larger size may have greater data transmission rate, but it also has a greater packet error rate. Conversely, the packet of smaller size has less packet error rate, but it also has a lower data transmission rate.
In the conventional wireless communication apparatus, the packet types of DM1, DH1, DM3, DH3, DM5 and DH5 are selectively used. Accordingly, there have been problems that the device cannot flexibly adapt to the change of packet error rates with respect to the transmitted data packet, and transmission efficiency deteriorates.